The winter jacket is made of foam polyethylene. The winter jacket should be fitted when the average outdoor temperature consistently falls below 5°C for a number of days, and removed when the temperature is constantly above 10°C, so is not always necessary in the majority of the UK.
It is essential that the winter jacket is removable during the process, otherwise the compost will burn, in which event the microorganisms die and the process is halted.
NB. Rake not included.